As a class of important endogenous small noncoding RNAs that regulate gene expression at the posttranscriptional level,
microRNAs (
miRNAs) play a critical role in many physiological and
pathological processes. It is believed that
miRNAs contribute to the development, differentiation, and synaptic plasticity of the neurons, and their dysregulation has been linked to a series of diseases.
MiRNAs exist in the tissues and as circulating
miRNAs in several body fluids, including plasma or serum, cerebrospinal fluid, urine, and saliva. There are significant differences between the circulating
miRNA expression profiles of healthy individuals and those of patients. Consequently, circulating
miRNAs are likely to become a novel class of noninvasive and sensitive
biomarkers. Although little is known about the origin and functions of circulating
miRNAs at present, their roles in the clinical diagnosis and prognosis of diseases make them attractive markers, particularly for
tumors and
cardiovascular diseases. Until now, however, there have been limited data regarding the roles of circulating
miRNAs in central nervous system (
CNS) diseases. This review focuses on the characteristics of circulating
miRNAs and their values as potential
biomarkers in
CNS diseases, particularly in
Alzheimer's disease,
Huntington's disease,
multiple sclerosis,
schizophrenia, and
bipolar disorder.